Merge branch 'js/check-null-from-read-object-file'

The code paths that call repo_read_object_file() have been
tightened to react to errors.

* js/check-null-from-read-object-file:
  Always check the return value of `repo_read_object_file()`

diff --cc bisect.c
Simple merge

diff --cc builtin/cat-file.c
Simple merge

diff --cc builtin/grep.c
Simple merge

diff --cc builtin/notes.c
Simple merge

diff --cc combine-diff.c
Simple merge

diff --cc rerere.c
Simple merge